The present invention relates to method and apparatus for encoding source data into a data block format composed of data words and parity check words derived from selected data words. The invention is particularly useful for purposes of editing digital audio signals recorded in magnetic recording medium.
Various attempts have been made to reduce the error rate of magnetically recorded digital signals due to dropouts which occur in the recording medium by encoding check words from source data to form a data block such that upon reproduction of the recorded signals errors may be detected and corrected. In the prior art attempts error correcting check words are inter-mixed with associated data words. This results in a substantial increase in redundancy with the attendant increase in high data density in a recording medium. Stated differently, the spatial frequency of the recorded data bits increases to the point where complex system would be required. The degree of redundancy is usually determined in considering the nature of source data such as video signal, audio signal or computer data or the like in relation to the error rate of the recording medium employed. It is of particular importance to design a data format of high error correction capability under the imposed limitations of redundancy.
Electronic editing, on the other hand, is currently employed because of its advantage in that it permits transcription of a recorded audio program from one tape to another without the need for cutting off the tapes and joining them together. Due to inherent fluctuations of tape drive systems, it is almost impossible to precisely join the data bits at the editing point which are spaced a distance of several micrometers. Thus it would be necessary to discard a full data block in which the editing point occurs since that block is rendered invalid as a whole. To avoid this problem, a prior art approach provides an interblock gap (IBG) between successive data blocks to permit a editing point to occur therein. This method, however, has poor coding efficiency.